Single-wall carbon nanotubes (SWNT), commonly known as “buckytubes,” have been the subject of intense research since their discovery due to their unique properties, including high strength, stiffness, thermal and electrical conductivity. SWNT are fullerenes consisting essentially of sp2-hybridized carbon atoms typically arranged in hexagons and pentagons. For background information on single-wall carbon nanotubes see B. I. Yakobson and R. E. Smalley, American Scientist, Vol. 85, July–August, 1997, pp. 324–337. Multi-wall carbon nanotubes are nested single-wall carbon cylinders and possess some properties similar to single-wall carbon nanotubes. However, since single-wall carbon nanotubes have fewer defects than multi-wall carbon nanotubes, the single-wall carbon nanotubes are generally stronger and more conductive. Additionally, compared to multi-wall carbon nanotubes, single-wall carbon nanotubes have considerably higher available surface area per gram of carbon.
However, the full potential of the properties of single-wall carbon nanotubes have not been fully realized due to the difficulty of dispersing the nanotubes. The problems associated with dispersing single-wall carbon nanotubes are due largely to their insolubility in most common solvents and their propensity to rope together in SWNT bundles and be held tightly together by van der Waals forces. Attempts have been made to dissolve and characterize SWNTs in various organic solvents such as dimethyl formamide (DMF) and n-methyl pyrrolidone. Some solubilization has been attained in common organic solvents, but solubilization was achieved by significantly modifying the single-wall carbon nanotubes, i.e. cutting the nanotube lengths (i.e. to a length in the range of about 100 to 300 nm, such as by sonication) and derivatizing the shortened tubes with covalently-bonded functional groups that enhance solubility. Uncut SWNTs have also been made soluble by ionic functionalization of the carboxylic acid groups present at the open edges of purified SWNTs. Solubilization of the carboxylated nanotubes with latter procedure was achieved in 4 to 8 days of heating at 120–130° C. in neat octadecylamine and exfoliated the SWNT bundles from large ropes (10–25 nm in diameter) to small ropes (2–5 nm in diameter). Details of this derivatization can be found in Chen, et al. J. Phys. Chem. B, 2001, 105, p. 2525–2528.
Films of single-wall carbon nanotube films having high conductivity can be used in a variety of applications, including electrodes for capacitors, supercapacitors, actuators and fuel cells. Fabrication of high modulus single-wall nanotube film products for these and other applications remains a major challenge.